The present invention relates to coating compositions. More particularly, the invention relates to coating compositions containing less than about 30 percent organic solvents and which are based on an ester-containing polyol and an amine-aldehyde resin.
In recent years the coatings industry has become increasingly interested in low organic solvent-containing coating compositions; that is, coating compositions which can be applied by conventional techniques such as spraying, dipping, roll coating, etc., without the use of a high content of volatile solvents. The use of such compositions presents several advantages, including high film build per application, economy of materials since normally the solvents are lost to the ambient surroundings, the alleviation of environmental control problems such as treatment of plant effluents to capture or destroy volatile solvents, and energy savings since less air needs to be heated to volatilize the solvents in the curing oven.
However, to be a viable coating material, the low organic solvent-containing coating composition must be capable of forming a film having at least several of those characteristics required of coatings, e.g., adhesion, flexibility, hardness, stain resistance, detergent resistance, solvent resistance, humidity resistance and durability.
Various prior art references do disclose coating compositions having reasonably high solids contents (and thus low organic solvent contents). For example, U.S. Pat. No. 3,553,284 to Riemhofer et al., issued Jan. 5, 1971, is directed to compositions comprising an aminoplast and a polyester of hexahydroterephthalic acid and a diol having adjacent hydroxy groups, e.g., ethylene glycol, butanediol-(2,3), or cyclohexanediol-(1,2). U.S. Pat. No. 3,852,375 to Biethan et al., issued Dec. 3, 1974, discloses an ester of (1) aliphatic polyol and aliphatic diols such as ethylene glycol and propane diol and (2) one or more aromatic or cycloaliphatic dicarboxylic acids and one or more saturated aliphatic dicarboxylic acids together with an aminoplast resin. U.S. Pat. No. 3,883,454 to Dhein et al, issued May 13, 1975, discloses a high solids coating composition comprising a blend of a melamine resin and a binder of an oligomeric alkyd resin of a polyalcohol and an aromatic dicarboxylic acid. As further disclosed in the aforementioned patent, the oligomeric alkyd resin has a hydroxyl number between 40 and 150 and a molecular weight of from 800 to 2000. The aforedescribed compositions are not fully satisfactory due to their high viscosities, low water-compatibility and/or unsatisfactory film characteristics.
U.S. Pat. Nos. 3,959,201 and 3,994,851 to Chang, issued May 25, 1976 and Nov. 30, 1976, respectively, also describe high solids containing coating compositions. U.S. Pat. No. 3,959,201 describes coating compositions based on hydroxyl-containing organic materials and aminoplast resins. Several hydroxyl-containing materials are described, including polyester polyol oligomers based on triol or higher alcohol and a monocarboxylic acid such as acetic acid. U.S. Pat. No. 3,994,851 describes coating compositions of ester-containing polyols and amine-aldehyde crosslinking agents. The ester-containing polyol is described as prepared from a polyol and a polycarboxylic acid. While such disclosed compositions are satisfactory, there is still a need for low organic solvent- and high solids-containing coating compositions possessing better and/or different desirable characteristics.
There has now been found coating compositions which have low organic solvent contents, yet which have low viscosities (and, therefore, are easy to blend, mix and apply) and generally possess good water-compatibility. Films formed from the compositions possess a desirable set of characteristics.
As used herein, all percents, parts and ratios are by weight unless otherwise stated.